01/26/2025
Week 8: The Biological Components of Soil (Part 2)
This week, we dove deeper into the specific types of fungi, bacteria, and other soil food web members, exploring why they are (or aren’t) present and what role they play in cycling nutrients for plants. Here’s a breakdown of some fascinating soil biology:
🌱 Types of Mycorrhizal Fungi:
1️⃣ Endomycorrhizae
• Lives inside root cells.
• Preferred by annual plants.
• The largest group, making up 90% of all identified fungi.
2️⃣ Ectomycorrhizae
• Forms a sheath around roots.
• Preferred by trees in high-altitude or cold climates.
• A smaller group, comprising about 5% of known fungi.
3️⃣ Endo-Ecto Mycorrhizae
• Both sheaths and enters roots.
• Preferred by softwood species.
• An even smaller subgroup.
4️⃣ Orchid Mycorrhizae
• Critical for orchid plants, which depend on this symbiotic relationship to survive.
5️⃣ Ericoid Mycorrhizae
• Helps acidic-soil perennials like blueberries and rhododendrons thrive.
❌ Non-Mycorrhizal Plants
Certain plants, like amaranth, broccoli, rhubarb, purslane, and mullein, don’t form partnerships with fungi. These plants are often indicators of oxidized or alkaline soil conditions dominated by actinobacteria. They produce antimicrobial compounds that inhibit fungal development.
✨ Spotlight: Arbuscular Mycorrhizal Fungi (AMF)
• A type of endomycorrhizal fungi that increases the root’s surface area by up to 10,000x!
• Partners with 90% of all plants, boosting nutrient absorption.
• Forms a relationship when a spore germinates near a root. The plant sends out specific exudates to attract the hyphae into its root.
• Arbuscules (specialized structures) form in days and last only 4–15 days, but their benefits can last for decades!
• Produces glomalin, a sticky protein that strengthens soil structure and sequesters 1/3 of all soil carbon.
🥊 Other Soil Food Web Members
• Protozoa: Single-celled organisms (ciliates, amoebas, and flagellates) that move in water films on soil aggregates. They graze bacteria and cycle nutrients to plants. Their presence signals active nutrient cycling.
• Nematodes: Microscopic, non-segmented worms that regulate soil populations. They feed on fungi, bacteria, protozoa, and other nematodes. While they mineralize soil and cycle nutrients, root-feeding nematodes indicate problematic soil conditions (dry or anaerobic).
• Micro-Arthropods: Invertebrates with jointed legs that live in the top 3 inches (7.5 cm) of soil. Classified as shredders, herbivores, predators, or fungal feeders. Their waste creates soil structure and boosts microbial activity. However, some herbivores are pests that feed on roots.
• Earthworms: Nature’s tillers! Found in most soils, they improve soil structure by tunneling and leaving nutrient-rich castings. Where earthworms are absent, enchytraeids perform similar functions.
• Macro-Arthropods: Larger invertebrates (like insects) with exoskeletons made of chitin. While some are pests, others are predators or decomposers that benefit soil health. Tools like diatomaceous earth can harm them, so use cautiously to avoid unintended effects.
• Birds and Small Mammals: Bring seeds, microbes, spores, and nutrients from other ecosystems. They act as predators, litter shredders, aerators, and fertilizers. Their manure speeds up the breakdown of mulch and leaf litter.
I know this is a lot of information, trust me I'm trying to keep it short and to the point but soil biology is fascinating and so complex. Every organism plays a role in creating a thriving ecosystem. Have you noticed any of these soil helpers in your garden? Let us know in the comments below!
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